Ernest p



(No Model.)

E. P. WARNER. ELBGTROMAGNETIG DAMPER FOR MEASURING INSTRUMENTS.

Patented Aug. 13,1895.

UNITED STATES PATENT, OFFICE.

ERNEST P. WARNER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE WESTERN ELECTRIC COMPANY, OF SAME PLACE.

ELECTROMAGNETIC DAMPER FOR MEASURING-INSTRUMENTS.

SPECIFICATION forming part of Letters Patent No. 544,332, dated August 13, 1895. Application filed September 18, 1894. Serial No. 523,333. (No model.)

To ail whom it may concern.-

Be it known that I, ERNEST P. WARNER, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Electromagnetic Dampers for Measuring-Instruments, (Case No. '57,) of which the following is a full, clear, concise, and exact description, reference being had to [o the accompanying drawings, forming a part of this specification.

My invention relates to that class of electrical measuring-instruments in which a magnetic vane or armatureis subjected to the ac- !5 tion of a solenoid surrounding the same and included in a circuit, a pointer or indicator being ordinarily attached to the armature to move over a graduated scale when the armature is actuated. In such instruments the needle or pointer is usually adapted to take the zero position under the influence of gravity when no current is passing through the coil. When current is established the armature is moved in opposition to the action of gravity, the amount of said motion depending on the ampere turns set up in the coil. In such instruments the needle has been liable to oscillate more than is desirable under changes in the ampere turns of the coil, ren- 0 dering it difficult to make a true reading, es-

pecially when the changes are sudden and extreme. By the use of my invention these objectionable oscillations are prevented and the instrument is rendered practically dead- 3 5 beat.

My invention, speaking generally, consists of a metallic disk, preferably of light metal, as aluminum, rigidly mounted upon the rotating-shaft, so that any motion of the arma- 0 ture will be accompanied by corresponding motion of the disk. This disk is located within the magnetic field of the coil, so that when rotated it will cut the lines of force and set up eddy-currents within itself. The re- 5 sult of these eddycurrents is to effect a retardation of the rotary movements of the disk, and consequently of the armature and needle, the amount of such retardation depending upon the rapidity of the movement and the number of lines of force out.

My invention will be more readily understood by reference to the accompanying drawings, in which-- Figure Us a front elevation of an ammeter provided with my electromagnetic damper. 5 Fig. 2 is a sectional view thereof on line 2 2, Fig. 1. Fig. 3 is a sectional view on line 3 3, Fig. 2.

Like parts are indicated by similar letters of reference throughout the difi'erent figures.

As is usual in this class of instruments the armature a and the needle b are pivoted upon an arbor c and counterbalanced, so that when no current is passing through the coil 01 the pointer or needle will indicate zero, as shown in Fig. 1. When current is sent through the coil d the armature, and consequently the needle, will be rotated, as indicated by the arrow.- The scale is graduated to indicate, in this instance, amperes. In case the coil is made up of fine wire and the instrument is used as a voltmeter, the scale will be graduated accordingly to indicate volts. As measuring-i'nstruments of this general construction are well known in the art, no further gen- 7 5 eral description thereof is deemed necessary.

My invention consists in the metallic disk e,.connected with the armature so as to move within the field of force when the armature is moved in response-to changes in current 89 passing through the coil d. This metal disk being rotated in the field will cut lines of force, and thus eddy-currents will be set up in the disk, causing the disk to offer more or less mechanical resistance to the oscillations 8 of the needle, according to the number of lines of force that may be cut by the disk. I have found that a metal plate which is of light metal, as aluminum, and which is disk-shaped and centrally pivoted upon the arbor carry- 90 ing the armature, is the most satisfactory. I do not, however, limit myself in all of my claims to any particular kind of metal or to the precise form of the disk shown and described, since it is evident that other metals 5 as, for example, copper, or even ironmight be successfully employed, and that the shape of the rotary damping plate or piece might be varied without injuriously' affecting the utility thereof. 10:)

mounted to rotate with said armature, the disk being adapted to rotate in its own plane and in front of the end of the coil to act as a damper, substantially as described.

In witness whereof I hereunto subscribe my name this 2d day of August, A. D. 1894-.

ERNEST P. WARNER. \Vitnesses:

GEORGE L. CRAGG, HARRIET G. TEMPLETON. 

